1. Field of the Invention
The present invention relates to jet propelled aircraft. Although the disclosure herein specifically relates to remotely controlled, flying scale model aircraft, the invention as disclosed and claimed herein may also be used on full size aircraft and for other related uses. In the scale model aircraft industry great efforts are taken to accurately reproduce the particular full size operational aircraft being modeled, both in appearance and operational characteristics. Although great strides have been achieved in the industry, one area affecting both appearance and scale model performance has been neglected; that being the jet exhaust nozzle. Operational full size jet aircraft of the present day are commonly equipped with exhaust nozzles having controllable variable area geometry; that is to say that the exit diameter of the jet nozzle may be varied depending upon the particular flight regime within which the aircraft is being operated. Two particular flight regimes that require different exhaust nozzle configurations, for both full size and scale model aircraft, are take-off and in flight cruse. Full size operational aircraft employ maximum exhaust nozzle diameters for take-off and decrease or restrict the exhaust nozzle diameter during in flight cruse. It is an established fact that jet propelled aircraft, full size or scale model aircraft, cannot have a cruising velocity, or air speed, greater than the exit velocity of the jet engine exhaust at the tail pipe exhaust nozzle. It is also established that the optimum exhaust nozzle configuration to produce maximum thrust at take-off (requiring a large diameter nozzle opening) is not optimum at cruse where less than take-off thrust is required to propel the aircraft at a constant velocity or air speed. Therefore, full size operational aircraft are equipped with variable area geometry exhaust nozzle whereby the diameter of the nozzle may be decreased or restricted to a smaller, more optimum, diameter for in flight cruse (thereby providing increased exhaust gas velocities permitting increased flight velocities) and open to full diameter or take-off and landing.
Scale model jet aircraft using ducted fan technology to obtain a propelling thrust from the exhaust nozzle, experience similar nozzle configuration problems as their full counterparts; that being that a large diameter exhaust nozzle configuration is desired for take-off however, a smaller or reduced diameter nozzle diameter is desired for in flight cruse.
2. Description of the Prior Art
U.S. Pat. No. 2,634,578 issued to G. W. Kallal on Apr. 14, 1953 for a "Device For Varying The Effective Area Of Discharge Orifices Of Jet Engines Or Afterburners Therefor" teaches a variable area jet exhaust nozzle which relies upon the high pressure gases within and exiting the nozzle to force the nozzle to its full open position. The nozzle exit diameter may be decreased by winding, upon a motor driven drum, a cable which is threaded through a series of guides circumferentially spaced about the external rearward periphery of the nozzle. Thus to convergingly reduce the nozzle exit diameter, the drum is rotated so as to wind in the control cable thereby reducing the nozzle exit diameter. To expand the nozzle exit diameter, a brake or other type of locking mechanism upon the drum is released thereby permitting the cable to unwind from the drum permitting the nozzle exit diameter to increase by action of the high pressure exhaust gases acting upon the inside surface of the nozzle. It is therefore apparent that the variable area nozzle as taught in the U.S. Pat. No. 2,634,578 can only be operated when the engine is operating and high pressures gases are flowing therethrough.
U.S. Pat. No. 4,850,535 issued to P. B. Ivie, on Jul. 25, 1989 for a "Variably Convergent Exhaust Nozzle For A Model Ducted Fan Unit" teaches a variable area exhaust nozzle for use on a scale model jet propelled aircraft wherein the nozzle comprises a multiplicity of circumferentially spaced apart, axially extending, inner leaves circumscribed by a multiplicity of, axially extending, overlapping spaced apart outer leaves. The outer leaves are affixed to hinges having hinge arms extending the full axial length of each leaf thereby providing structural rigidity to each outer leaf. Threaded through guides at the rearward end of each hinge arm is one of two control cables; each cable controlling half of the hinge arms or 180 degrees of the nozzle. The control cables are attached to a servo motor that, when the control cables are pulled taught, the diameter of the nozzle exit end is caused to constrict or decrease.
Similar to the nozzle taught in U.S. Pat. No. 2,634,578, discussed hereinabove, the nozzle of U.S. Pat. No. 4,850,535 has no positive mechanical means for opening the nozzle to its full divergent configuration. Both nozzles must rely upon gas pressure, within the nozzle, to return the nozzle to its full open position.